Dyeing methods utilizing oxidation dyeing agents such as phenylenediamines and aminophenols are frequently used in dyeing of keratin fibers, specifically human hairs and the like, by utilizing the advantages that dyeing is possible in various color tones, lasts long, and doesn't take much time, and the like. On the other hand, indole analogues are also utilized as oxidation dyeing agents for dyeing keratin. For example, an indole derivative 5,6-dihydroxyindole is a melanin precursor and polymerizes in the presence of oxygen to form a melanin pigment. It is possible to dye hairs and the like by utilizing this reaction. For example, Patent Documents 1 and 2 disclose air oxidation-type dyeing agents utilizing indole derivatives such as 5,6-dihydroxyindole.